1. Field of the Invention
The present invention relates to a probe needle for a probe card and a fabrication method thereof. More particularly, the present invention relates to a probe needle for a vertical needle type probe card and a fabrication method thereof.
2. Description of the Background Art
Among the processes of fabricating an IC, an LSI and the like, a wafer test process is known to test whether each chip on a wafer is an acceptable product or not. In this wafer testing, a probe card is generally attached to a device called a prober. The test is carried out by placing the probe needle of the probe card on a predetermined pad (electrode) on the wafer chip (referred to as overdrive operation) with at least a predetermined pressure (referred to as stylus pressure) to form contact. More specifically, a probe card is developed to test the electrical characteristics of a semiconductor device in the fabrication process of a semiconductor device. This probe card includes the conventional vertical needle type probe card. Particularly, a cobra probe card developed by IBM has attracted a wide range of attention, and is now beginning to be used for practical usage.
FIG. 8 is a schematic diagram showing a conventional cobra probe card. Referring to FIG. 8, the upper end of a cobra type probe needle 101 is attached in a vertical manner to an upper guide plate 102 in this conventional probe card. Also, a lower guide plate 103 for positioning an electrode 109 that will form contact with probe needle 101 is located beneath upper guide plate 102. A through hole 104 is provided in lower guide plate 103 to guide probe needle 101. The upper end of probe needle 101 is connected to a terminal (not shown) arranged around upper guide plate 102 via a wiring (not shown). The leading end of probe needle 101 forms contact with electrode 106 provided at the surface of a semiconductor device that is the subject of testing. This probe card is used to test the electrical characteristics of a semiconductor device.
FIG. 9 is a schematic diagram for describing an operation of the probe needle of the cobra probe card shown in FIG. 8. Referring to FIG. 9, an external force 105 is exerted to bring probe needle 101 in contact with electrode 109. External force 105 is exerted onto this probe card in the direction indicated by the arrow in FIG. 9. When leading end 107 of probe needle 101 is in contact with electrode 109, a portion 108 fixed to upper guide plate 102, a portion 106 guided by lower guide plate 103, a bent portion 111 absorbing the stress, and leading end portion 107 of probe needle 101 in contact with electrode 109 are arranged as shown in FIG. 9.
The above-described probe needle 101 of the conventional cobra type probe card has two problems set forth in the following.
The first problem is that a great deflection is generated at bending portion 111 when leading end 107 of probe needle 101 is brought into contact with electrode 109 since bending portion 111 is formed so as to absorb the stress at that one portion. When leading end 107 of probe needle 101 is brought into contact with electrode 109, probe needle 101 will contact the side surface of through hole 104 in lower guide plate 103. As a result, the side surface of through hole 104 is scraped to generate scraps. The scraps will block through hole 104 to degrade the passage of probe needle 101. Furthermore, probe needle 101 will be caught at the side surface of through hole 104 due to the friction between probe needle 101 and through hole 104. There is a possibility that probe needle 101 will be stuck in through hole 104 so as not to protrude therefrom. Therefore, the height level of each leading end 107 of each the plurality of probe needles 101 will differ to result in step-graded levels. This means that there is variation in the penetration pressure of probe needle 101 to project into an aluminum oxide film (not shown) formed on electrode 109. The contact pressure between electrode 109 and leading end 107 of probe needle 101 will become improper, so that testing of the electrical characteristics cannot be carried out at high accuracy.
The second problem is that the stress is concentrated at one bending portion 111 of probe needle 101 when leading end 107 of probe needle 101 forms contact with electrode 109 since probe needle 101 is formed so that the stress is absorbed at only one bending portion 111. Repetitive usage with the stress always concentrated at one location will cause metal fatigue due to the repetitive loading. Probe needle 101 was sometimes broken into two pieces or permanently bent. Thus, the lifetime of probe needle 101 becomes shorter. This was not cost effective since extra cost is required for the exchange.